Maxillary palps can mediate taste rejection of plant allelochemicals by caterpillars |
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Authors: | J I Glendinning S Valcic B N Timmermann |
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Institution: | (1) Arizona Research Laboratories, Division of Neurobiology, The University of Arizona, Tucson, AZ 85721, USA, US;(2) Department of Pharmacology and Toxicology, The University of Arizona, Tucson, AZ 85721, USA, US |
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Abstract: | All caterpillars possess a pair of maxillary palps that “drum” the surface of foods during feeding. These chemosensory organs
contain over 65% of a caterpillar's taste receptor cells, but their functional significance remains largely unknown. We examined
their role in rejection of plant allelochemicals, using the tobacco hornworm (Manduca sexta) as a model insect and an extract from a plant species (Grindeliaglutinosa) as a model stimulus. We selected this system because hornworms reject foods containing Grindelia extract, and because preliminary studies indicated that their maxillary palps respond to this extract. We hypothesized that
Grindelia extract elicits rejection through stimulating: (1) olfactory receptor cells, (2) taste receptor cells, (3) oral mechanoreceptors,
and/or (4) a postingestive response mechanism. Our results were consistent only with hypothesis 2: caterpillars approached
Grindelia-treated diets without apparent hesitation, but rejected it within 6 s of initiating biting; Grindelia-treated solutions stimulated taste receptor cells in the maxillary palp, but not the other gustatory chemosensilla; and ablating
the maxillary palps eliminated rejection of Grindelia-treated diets. Our results demonstrate that taste receptor cells in the maxillary palps mediate rejection of Grindelia extract, and provide the first direct evidence for a role of maxillary palps in rejection of plant allelochemicals.
Accepted: 25 January 1998 |
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Keywords: | Taste receptor cell Maxillary palp Feeding behavior Caterpillar Plant resin |
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